JPS6342351A - Manufacture of chromium-containing molten iron - Google Patents

Abstract

PURPOSE:To reduce manufacturing costs by using scrap as iron source, chromitite as chromium source, and carbon material as heat source and by controlling C content in molten iron and temp. of molten iron to specific values, respectively, at the time of manufacturing chromium-containing molten iron. CONSTITUTION:Steel scrap 5 is introduced into a melting-reducing furnace 1 of converter type, into which, from a furnace-bottom tuyere 1a, pulverized coal 2 and a powder of quick lime 4 as slagging agent are blown together with inert gas 11 of Ar, N2, etc., and also O2 gas 3 is blown simultaneously so as to burn the pulverized coal 2 by oxidation into CO and also to melt the scrap 5 by means of the above heat of oxidation. Hot blasts are generated in regenerators 6, 6' by waste-gas utilization and they are blown into the upper space of the furnace 1 to burn CO into CO2, so that temp. of molten iron and C content in molten iron are regulated to 1,500 deg.C and >=2.5%, respectively. Subsequently, chromitite and lump coke are charged from the upper part of the furnace, and Cr2O3 and FeO in the ore are reduced to form a chromium- containing molten iron metal with about 18% Cr content, which is desulfurized by blowing CaC2 blowing. In this way, the chromium-containing molten iron can be manufactured inexpensively.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention uses scrap as the main source of iron, and uses heat generated by oxidation of carbonaceous materials as a heat source to produce chromium-containing molten iron by adding chromium ore during melting and refining. It relates to a manufacturing method.

[Prior art] In recent years, the steel industry has developed a reactor iron manufacturing method (Japanese Patent Publication No. 59-4), which uses scrap as a raw material for iron manufacturing and utilizes the heat generated by oxidation of carbonaceous materials instead of an electric furnace to manufacture steel.
No. 4363) and the like have been proposed and disclosed. This energy saving movement is spreading not only to ordinary steel but also to stainless steel.

Traditionally, stainless steel has been produced by charging scrap and ferrochrome as a chromium source into an electric furnace and melting it with an electric heat source, but recently, carbon materials and oxygen have been injected into the electric furnace and reacted. There are methods for reducing electricity consumption by using heat, and methods for retaining chromium in the melt by adding chromium ore when pre-dephosphorized hot metal is smelted in a converter and melting it down. Publication No. 56-2125) etc. have been proposed and disclosed.

[Problems to be solved by the invention] In the production of stainless steel using a conventional electric furnace, scraps generated in the steel mill, processed scraps recovered from cloth, and even waste scraps are contained in the recovered scraps. Considering that the method of using chromium as a chromium source is cheaper than using ferrochrome, we mainly use the same type of scrap containing chromium as the main iron source, and use ordinary steel scrap and ferrochrome as a chromium source to make up for the shortage. The mainstream is the chromium recycling method, which has fewer raw material constraints and low raw material costs.

However, as described above, this method uses electricity as a heat source for melting scrap and ferrochrome, and therefore has a problem in that high electricity charges increase manufacturing costs.

On the other hand, in the method of smelting and reducing chromium ore using pre-dephosphorized hot metal as a base, converter blowing is the main process, making it possible to produce chromium-containing molten iron without using electricity. ing. Moreover, the chromium ore is melted down and retained in the molten steel, making it possible to significantly lower the cost of the chromium source compared to using ferrochrome produced in a separate electric furnace. However, this method uses hot metal as the main source of iron, which requires preliminary dephosphorization, and the lack of heat supply limits the use of chromium-containing scrap. had.

Under these circumstances, the objectives of the present invention are: - to use scrap as the main source of iron; - to use heat generated by the oxidation of carbonaceous materials as a heat source without relying on electricity; and - to replace scrap chromium as a source of iron. An object of the present invention is to provide a method for producing chromium-containing molten iron that can obtain chromium-containing molten iron at a low cost by satisfying three conditions: chromium and/or chromium ore are obtained by melting and reduction.

[Means for Solving the Problems] The present invention, which has solved the above problems, uses scrap as the main source of iron, and adds carbonaceous material and oxidizing gas to the furnace to remove at least the carbonaceous material. The iron source is oxidized to CO, and the oxidation heat at this time melts the iron source, and the molten iron after melting has [C] ≧2.5% (%: weight %, the same applies hereinafter).
The gist of the structure is to melt and reduce the separately added chromium ore by adjusting and maintaining the molten iron temperature at 1500° C. or higher.

[Operations] As mentioned above, in the process of manufacturing chromium-containing molten iron using scrap as the main iron source, including stainless steel, ■ the melting energy of scrap is converted from current electric power to the oxidation exothermic energy of inexpensive carbonaceous materials. (1) Use of an inexpensive ROM source are essential prerequisites for reducing manufacturing costs.

Currently, chromium sources include chromium in scrap,
Ferrochrome manufactured in a separate electric furnace is used, but if this ferrochrome can be replaced with chromium ore, melted and reduced with carbonaceous material, and directly retained in molten steel, manufacturing costs can be reduced. We hope that this will have a great impact on the future. However, chromium ore (M
g.

)-e) O. (Cr, A1.Fe) Since it is a difficult ore consisting of chromite spinel with a composition of 203 and serpentine with a high melting point, operating conditions must be set appropriately to obtain a high chromium yield. There is a need.

It was found that the carbon concentration in molten iron and the temperature of molten iron have a large influence on the smelting reduction rate of chromium ore. Figure 1 shows the relationship between the carbon concentration in molten iron and the smelting reduction rate of chromium ore, but since the chromium ore smelting reduction rate changes greatly after the carbon concentration in molten iron reaches 2.5% (for details, see 2 when the molten iron temperature is 1550℃~1600℃
．． 5% and 2 when the molten iron temperature is 1600℃~1650℃
In order to obtain a high rate of smelting and reduction of chromium ore (which varies rapidly in percentage), it is necessary to maintain the carbon concentration in the molten iron at 2.5% or more on the safe side. In addition, regarding the relationship between molten iron temperature and chromium ore melt reduction rate,
As shown in the figure, the smelting reduction rate changes greatly around 1500'C, so the molten iron temperature must be set to 1500 or above in order to obtain a high smelting reduction rate.

On the other hand, in the process of adding carbonaceous substances and oxidizing gas to oxidize the carbonaceous substances to CO and some CO□, and melting the scrap with the heat of oxidation at this time, in order to obtain operational stability, it is necessary to It is necessary to maintain the carbon concentration in the molten iron at a high level of about 2%, and the carbon concentration in the molten iron is 2%.
If it is lower, as shown in FIG. 3, the concentration of T-Fe, that is, iron oxide in the slag becomes high, causing slag foaming and a decrease in iron yield. Also, the temperature of molten iron is 1450-150
The temperature must be around 0°C.

Therefore, the process of melting the scrap by the heat of oxidation of the carbonaceous material and f! 1! When operating in combination with the process of melting and reducing chromium ore as hot water, it is necessary to set the above conditions regulated by the present invention, so that both processes can be organically combined and carried out efficiently. Can be done.

Further, when chromium ore is melted and reduced, a large amount of slag is generated from the slag-forming agent and gangue of the ore. Therefore, if the scrap is melted at this time, the melting of the scrap will be inhibited by the slag. Therefore, it is desirable to reduce the chromium ore by melting it after the melting of the scrap has been completed or at least % has been completed.

As a chromium source, in addition to chromium in scrap and/or chromium ore, pellets pre-reduced in a rotary kiln or the like may be used. In this case, not only the reduction time is shortened, but also the amount of carbonaceous material and oxidizing gas used is reduced because the amount of heat absorbed during reduction is reduced. Furthermore, if necessary, chromium-containing molten iron with a desired content can be obtained by obtaining a chromium source from chromium in scrap and supplementary addition of chromium ore.

In the present invention, since a large amount of carbonaceous material is used as the main heat source, sulfur contained in ordinary carbonaceous materials enters the molten iron. Therefore, when producing chromium-containing molten iron such as ordinary stainless steel, desulfurization must be performed, and decarburization is also necessary to produce molten steel.

Desulfurization is carried out after the smelting reduction of the chromium ore when the use of carbonaceous material is completed. At this time, the carbon concentration in the molten iron was 2.5%.
Since the molten iron is higher than the above, the reactivity of sulfur in the molten iron is high and desulfurization becomes easy. Therefore, maintaining a high carbon concentration during melt reduction of chromium ore is essential for efficient subsequent desulfurization. During the desulfurization period, the injection of carbonaceous substances that serve as sulfur sources and oxidizing gas that inhibits desulfurization, which is a reduction reaction, must be stopped, and the molten iron must be stirred using an inert gas such as nitrogen.

After desulfurization, slag with a high sulfur concentration is removed, and then oxidizing gas is blown into the steel to decarburize it and produce crude molten steel.

In addition, since chromium in molten iron increases the saturation solubility of nitrogen in molten iron, it is necessary to perform some denitrification treatment, but a large amount of CO gas is generated during the decarburization period, and this CO gas bubbles can be used to simultaneously denitrify. It can be carried out. Figure 4 shows the relationship between the amount of decarburization in molten iron and the nitrogen content in hot metal. It is necessary to set the amount of decarburization according to the required nitrogen level, but in any case, maintaining the carbon concentration at 2.5% or more in the previous step is an essential condition for denitrification.

As described above, in the process of producing chromium-containing molten iron by adding chromium ore as a chromium source during melting and refining of scrap as the main iron source, oxidation of carbonaceous substances and oxidizing gases as regulated by the present invention. By using heat to melt scrap and reduce the chromium ore by melting, followed by desulfurization and decarburization, and controlling the carbon concentration in the molten iron and the molten iron temperature during the process, the entire process is organically linked. This enables a streamlined process, lower manufacturing costs, and stable operation.

[Example] Using the scrap melting and refining furnace shown in FIG. 5 (schematic diagram), chromium-containing molten iron (18% Cr) was manufactured according to the manufacturing flow diagram and conditions shown in FIG. 6. 1 is a melting and refining furnace (
(hereinafter referred to as a furnace), pulverized coal is used as the carbonaceous material, pulverized coal 2 and quicklime 4 are introduced together with an inert gas 11 by bottom blowing, and oxygen 3 is introduced as an oxidizing gas into the furnace 1 from the lower part 1a of the furnace. Then, the pulverized coal is oxidized and burned with oxygen to at least CO, and the scrap 5 is melted by the oxidation heat.

Furthermore, a heat storage chamber 6.6' is provided, whereby hot air is produced and blown into the upper space of the furnace 1 to oxidize and burn a part of the CO gas to CO2, and the heat causes the squirrel scrap 5 to further melt. The molten iron temperature at this time was 1500°C, and the C content in the molten iron was 3%. Roughly, chromium ore and lump coke are charged into the furnace 1 while adjusting and maintaining the temperature of [C]≧2.5% in the molten iron and 1500° C. or higher, and the chromium ore is melted and reduced. In order to obtain even higher quality chromium-containing molten iron, the introduction of pulverized coal 2 and oxygen 3 was temporarily stopped, and quicklime 4, calcium carbide 7 and inert gas 12 were introduced to perform desulfurization, and then oxygen 3 was blown in. Decarburize to obtain chromium-containing molten iron.

In addition, high-temperature exhaust gas is stored in a heat storage chamber 6.6', an exhaust heat boiler 8,
9. The scrap preheating device 1o exchanges heat and is used for producing high temperature air and steam, preheating scrap, etc.

Table 1 shows the main unit consumption when producing 18%Cr crude molten steel by the above-described method as an example, and the unit consumption when producing it in a normal electric furnace as a comparative example.

Table 1 shows that it is possible to replace electricity with carbonaceous materials and replace ferrochrome with chromium ore, making it possible to significantly reduce costs.

Table 1 [Effects of the Invention] As described above, according to the method of the present invention, 1) scrap is used as the main iron source, 2) heat generated by oxidation of carbonaceous material is used as a heat source without relying on electricity, and 2) chromium source is used. Molten chromium iron can be obtained at low cost by obtaining it from smelting reduction of chromium and/or chromium ore in scrap.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the carbon concentration in molten iron and the smelting reduction rate of chromium ore, Figure 2 is a diagram showing the relationship between molten iron temperature and the smelting reduction rate of chromium ore, and Figure 3 is a diagram showing the relationship between [T-Fe] in slag and the smelting reduction rate of chromium ore. Figure 4 is a diagram of the relationship between the carbon concentration in molten iron, the amount of decarburization of molten iron and the nitrogen content in hot metal, Figure 5 is a schematic diagram of the scrap melting and refining furnace used in the examples, and Figure 6 is FIG. 2 is a flow diagram illustrating an embodiment of the present invention. Engineering: Melting and refining furnace 2: Pulverized coal 3: Oxygen 4: Quicklime 5: Scrap
6... Heat storage chamber 7... Calcium carbide 11.12... Inert gas 13... Hydrocarbon gas

Claims (1)

[Claims] (1) Using scrap as the main source of iron, carbonaceous material and oxidizing gas are added to the furnace to convert the carbonaceous material into at least Co.
At the same time, the oxidation heat at this time melts the iron source, and the molten iron after melting is adjusted to [C] ≧ 2.5% (%: weight %, the same applies hereinafter) and the molten iron temperature is maintained at 1500°C or higher. A method for producing chromium-containing molten iron, which is characterized by melting and reducing chromium ore that is separately added.